<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <canvas id="cont" width="1000px" , height="1000px">您的浏览器版本太低，不支持画布，请更新浏览器</canvas>
    <script>
        //固定的两步
        var canvas = document.querySelector('#cont')
        var ctx = canvas.getContext('2d')
        ctx.beginPath()
        ctx.arc(200, 200, 120, 0, Math.PI*2, false)
        ctx.strokeStyle = 'red'
        ctx.stroke()

        ctx.beginPath()
        ctx.arc(200, 200, 150, 0, Math.PI*2, false)
        ctx.strokeStyle = 'red'
        ctx.stroke()

        ctx.beginPath()
        ctx.arc(200, 200, 180, 0, Math.PI*2, false)
        ctx.strokeStyle = 'red'
        ctx.stroke()


    </script>
</body>

</html>